Rechargeable batteries are commonly used in electrical appliances such as mobile phones, electric shavers and portable music systems. It is well known that to maximise battery performance and to prolong the life of the battery, as measured by the number of charge/discharge cycles, that the battery must be fully discharged before being fully charged. However, for convenience, it is preferable to keep the battery in a state of constant readiness, that is, always fully charged. Therefore, it is common practice to charge a partially drained battery. This causes the battery performance to deteriorate, and the battery is said to exhibit a "memory effect".